Rectangular to circular waveguide coupler



May 3i, 1960 A. D. BERK 2,939,094

RECTANGULAR TO CIRCULAR WAVEGUIDE COUPLER Filed Aug. 2, 1956 INVENTOR. ARISTED D. BERK,

ATTORNEY.

United States Patent RECTANGULAR TO CIRCULAR WAVEGUIDE COUPLER Aristid D. Berk, Pacific Palisades, Calif., assignor to Hughes Aircraft Company, Culver City, Caliii, a cor-' poration of Delaware Filed Aug. 2, 1956, Ser. No. 601,666

6 Claims. (Cl. 3333-21) This invention relates to a rectangular to circular waveguide coupling device with controllable polarization and more particularly to a rectangular to circular waveguide coupling device which utilizes the properties of an element composed of a ferrite material to electrically control the polarization of the electromagnetic wave launched in the circular waveguide.

It is generally known that a ferrite material provides a medium throughout which numerous spinning electrons are distributed. These spinning electrons may be considered to be magnetic dipoles; When the ferrite material is immersed in a direct-current magnetic field, the magnetic dipoles are aligned parallel to the magnetic field, i.e., the axes of rotation of the rotating electrons are parallel to the magnetic field. Further, a circularly polarized electromagnetic field that is transverse to the direct-current magnetic field has the effect of rotating the magnetic dipoles about the lines of force of the direct-current magnetic field, thereby producing a precession. When the precessional velocity of the magnetic dipoles about the magnetic lines of force is substantially equal to and in the same direction as the rotating magnetic field portion of the electromagnetic wave, a phenomenon occurs that is known as gyro-resonance. When gyro-resonance exists, the magnetic dipoles tend to precess about the magnetic lines of force at progressively increasing angles and in so doing constitute current flowing in circular paths throughout the medium of the ferrite material.

In accordance with the present invention, a direct-current magnetic field is produced lengthwise through a ferrite rod, one portion of which is inserted through an aperture in the center of at least one of the broad sides of a rectangular waveguide and another portion of the rod inserted coaxially into a length of circular waveguide. Further, the direct-current magnetic field through the ferrite rod is provided by means of a yoke which commences at "ice This rotation constitutes a flow of current along circular paths, which current flow excites a wave of electrically the remaining broad side opposite the aperture through 1 which the ferrite rod is inserted and extends to and substantially surrounds a portion of the circular waveguide a short distance past the termination of the ferrite rod. A suitable number of ampere-turns are disposed around this yoke to produce a magnetic field of an intensity to cause gyro-resonance to exist in the ferrite rod at the frequency of operation of the coupling device.

As is generally known, the center portion of an electromagnetic wave propagated by a rectangular waveguide may be considered as two oppositely rotating circularly polarized waves of equal energy. The ferrite rod couples to a selected one of these circularly polarized waves, as determined by the direction of the direct-current magnetic field therethrough. When a portion of the length of the ferrite rod is immersed in a circularly polarized electromagnetic lield, so-called exchange forces, i.e., dipoledipole coupling forces, couple the magnetic dipoles not in the circularly polarized electromagnetic field to the precessing magnetic dipoles in the circularly polarized field so that they rotate at the same precessional velocity.

controlled polarization in the circular waveguide.

It is therefore an object of the present invention to utilize the characteristics of a ferrite material to provide coupling of electromagnetic energy from a rectangular to a circular waveguide.

Another object of the invention is to provide a device for coupling substantially one-half the electromagnetic energy propagated by a rectangular waveguide to a circular waveguide, the polarization of the electromagnetic energy launched in the circular waveguide being electrically controllable. V

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent by reference to the following dc scription taken in conjunction with the accompanying drawing, wherein:

Fig. l is a schematic perspective view of an embodiment of the device of the present invention;

Fig. 2 is a top view of the device of Fig. 1 together with apparatus for producing the direct-current magnetic field indicated therein; and

Fig. 3 is a side view of the apparatus shown in Fig. 2 with a cutaway section in the waveguide to illustrate the position of the ferrite rod.

Referring now to the drawing, Fig. 1 shows a perspective view of one embodiment of the present invention which comprises a section 10 of rectangular waveguide through which electromagnetic energy is propagated, and a section 12 of circular waveguide to which it is desired to couple electromagnetic energy being propagated by the rectangular section 10. The circular section 12 of waveguide is disposed normal to one of the broadsides of the section 10 of rectangular waveguide in a manner such that its longitudinal axis intersects the centerline of the broadside. An aperture 1-4 of a diameter sutficient to accommodate a ferrite rod 16 is disposed in the broadside concentrically about the longitudinal axis of the circular waveguide 12.

The ferrite rod 1-6 is preferably of a cylindrical configuration which for-the X-band range of frequencies would have a length of the order of 0.400 inch and a diameter of 0.100 inch. In the event that it is desired to have a narrow gyro-resonance range, the rod 116 may be composed, for example, of the ferrite material known commercially as Ferramic G. On the other hand, if it is desired to have a broad gyro-resonance rangeto facilitate operation over a broader range of frequencies and to have less critical operation, the rod 16 may be composed of the ferrite material known commercially as Ferroxcube 106. The ferrite rod 16 is disposed transversely across the rectangular waveguide section 10 whereby it protrudes a distance of the order of 0.1 inch'coaxially into the circular section 12 of waveguide. In accordance with the invention, a magnetic field represented by the vector H is produced lengthwise through the ferrite rod 16. The intensity of this magnetic field is such as to produce gyro-resonance within the ferrite material of the rod 16 at the frequency for which the device is to operate. This magnetic field H is of the order of 5000 Gauss and may be produced by means of a yoke 20 as shown in Figs. 2 and 3.

Referring to Figs. 2 and 3, yoke 20 includes a cylindrical portion 22-, one extremity of which is beveled to the extent that the cross-sectional area at the end is substantially equal to the cross-sectional area of the cylindrical rod 16. The opposite end of the cylindrical portion 22 is magnetically connected to arms 24 and 26 which extend outwards and around the rectangular waveguide 10 and then inwards in a manner to substantially surround the cylindrical waveguide section 12 slightly above the. termination. of the ferrite rod 16. To this. 7

end, the arms 24, 26 areprovided with semicircular notches of a diameter equal to outside diameter of circular waveguide .12. A symmetrical'path intermediate the .ferrite' rod 16 and the yoke 20 is thereby provided for the magnetic flux. It is realized that this may be accomplished by low reluctance paths of other configura tions The disclosed embodiment of the present invention,

however, requires that the termination of the yokeiil substantially surround the circular waveguide 12. Thus, it is evident that a single arm yoke with a ring circumventing the circular waveguide 121 could also be employed.

The magnetic field is developed lengthwise through the ferrite rod 16 by means of a coil 28 disposed about the cylindrical portion 22 of the yoke 20. This coil 28 is connected'through a reversing switch 30 across the terminals of battery 32.

In operation microwave energy is, propagated by the rectangular section 10 of the waveguide in a transverse electric mode. The magnetic field component of the fundamental transverse electric mode and for any Odd harmonic thereof is always linearly polarized. at the center of the waveguide. Hence, the ferrite cylinder :16 is immersed in a practically linearly polarized microwavefrequency magnetic field. This magnetic field may be resolved into two equal and opposite rotating, magnetic vectors. Because of the well known property of magnetized ferrites, only one of the two rotating vectors will induce large circulating magnetic currents within the ferrite rod 16. As previously pointed out, these circulating currents will not be confined to the portion of the length of the ferrite rod 16 within the rectangular waveguide 10, but will extend into the portion of the rod 16 which protrudes into the circular wave guide 12. The circulating magnetic currents will excite a rotating mode in the circular waveguide 12. If the frequency is chosen properly with respect to the inside diameter of the. circular waveguide 12, a'TE mode will be excited in TE mode in the circular waveguide 12 is determined by the direction of the direct-current magnetic field within the rod 16 and may be reversed by reversing the direction of the flow of current through the coil 28 by means 'of the reversing switch 30.

An obvious variation of the device described in connection with Figs. 2 and 3 is to replace the circular waveguide 12 with a cylindrical cavity. Rotating modes of one or of' the opposite sense may then be excited in the cylindrical cavity by reversal of the direct-current magnetic field H which may be accomplished by means ofthe reversing switch 30. To this extent the cylindrical waveguide 12 may be regarded as the equivalent of a cylindrical cavity. While the principle of the invention has been described above in connection with a specific embodiment, it is to be understood that this description is V wherein said direct-current magnetic field produced lengthmaterial disposed substantially around said circular wavethe circular waveguide. The sense of the rotation of the a circular waveguiding structure disposed normal to and,

electrically terminated in the plane of said one broad side of said rectangular waveguiding structure, the center line of said circular waveguiding structure extending coaxially through said aperture; a ferrite rod disposed transversely across said rectangular waveguiding structure and protrudguiding structure and commencing at a point therealong subsequent to the termination of said ferrite rod protruding therein, and means for providing at least one low reluctance path between said' .pole piece and said ring of ferromagnetic material; j 7

5. In a microwave coupler, the combination comprising a rectangular'waveguide for propagating electromagnetic energy in a transverse electric mode having a linearly polarized component of magnetic field transverse to the longitudinal center line of a broad wall, a circular waveguide terminated at one end at said broad wall with the longitudinal axis thereof perpendicuiar to the center line of said broadwall and aligned therewith, a ferrite rod disposed coaxially within said circular waveguide and extended through an aperture insaid broad wall into said rectangular waveguide for substantialiy the distance between broadwalls thereof, and means disposed; adjacent said ferrite rod for establishing a static magnetic 'field longitudinally therethrough and having a value to produce gyro-resonance at the frequency of said electromagnetic energy whereby said circular waveguide is excited by energy circularly polarized one sense by said ferrite rod as immersed in said linearly polarized magnetic field within said rectangular waveguide and subjected to said static magnetic field transverse to said linearly polarized magnetic field. V

6. The combination of claim 5 wherein said means for establishing a static magnetic field through said ferrite rod includes means for reversing the direction of said staticmaguetic field whereby the polarization of energy excited in said circular waveguide is reversed.

References Cited in the-file 'of this. patent UNITED STATES PATENTS 2,619,539 'Fano Nov. 25, 1952 2,768,354 Hogan Oct. 23, 1956 2,798,205 Hogan July 2, 1957 2,849,683 Miller Aug. 26, 1953 2,849,687 Miller Aug. 26, 1958 V FOREIGN PATENTS 64,770 France June 29, 1955 (Addition to original 1,079,880) r r OTHER REFERENCES Damon: Journal of Applied Physics, vol. 26, No. 10,

Oct. l955 pages 1281-1283.

Fox et al.: Bell System Technical Journal, (pages 74-76 7 relied on) 

